Firstly it is not entirely sensible to be giving the IUSR_<whatever> administrator rights even just for testing purposes.

The usual way to be running an application such as MS-WORD using DCOM is to be creating a specific (but normal interactive) user which it is to be run as and then give that users credentials on the identity tab in dcomcnfg - the caveat with running an application in this way is that the users registry hive is not loaded so any printers,network shares or whatever that may have been created for the user when they login interactively will not be created. A way round this that I have used before is to create a windows service (one that does absolutely nothing will be fine) that runs as this user - that way the registry hive will be loaded and kept open.

You will probably find this document useful

/J\